Bluetooth: Host: Deprecate BT_BUF_ACL_RX_COUNT symbol

Because the number of ACL RX buffers must be at least the number of
maximum connections plus one, increasing `CONFIG_BT_MAX_CONN` could
inadvertently lead to a build failure if the number of ACL RX buffers is
not also increased. This dependency may not be obvious to users.

To address this issue, this commit deprecates the
`CONFIG_BT_BUF_RX_COUNT` Kconfig symbol and computes the value in
`buf.h` using the new `BT_BUF_RX_COUNT` define. Note that the default
value and the minimum range value have been changed to 0 to "disable"
the option.

Additionally, to allow users to increase the number of ACL RX buffers,
this commit introduces the new `CONFIG_BT_BUF_RX_COUNT_EXTRA` Kconfig
symbol. The value of this symbol will be added to the computed value of
`BT_BUF_RX_COUNT`.

The configurations of tests and samples have been updated to reflect
these changes.

Signed-off-by: Théo Battrel <[email protected]>
(cherry picked from commit 66ff97e)
Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: theob-pro

include/zephyr/bluetooth/buf.h

@@ -88,13 +88,41 @@ struct bt_buf_data {
 #define BT_BUF_ISO_RX_COUNT 0
 #endif /* CONFIG_BT_ISO */
 
+/* see Core Spec v6.0 vol.4 part E 7.4.5 */
+#define BT_BUF_ACL_RX_COUNT_MAX 65535
+
+#if defined(CONFIG_BT_CONN) && defined(CONFIG_BT_HCI_HOST)
+ /* The host needs more ACL buffers than maximum ACL links. This is because of
+  * the way we re-assemble ACL packets into L2CAP PDUs.
+  *
+  * We keep around the first buffer (that comes from the driver) to do
+  * re-assembly into, and if all links are re-assembling, there will be no buffer
+  * available for the HCI driver to allocate from.
+  *
+  * TODO: When CONFIG_BT_BUF_ACL_RX_COUNT is removed,
+  *       remove the MAX and only keep (CONFIG_BT_MAX_CONN + 1)
+  */
+#define BT_BUF_ACL_RX_COUNT                                                                        \
+	(MAX(CONFIG_BT_BUF_ACL_RX_COUNT, (CONFIG_BT_MAX_CONN + 1)) +                               \
+	 CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA)
+#else
+#define BT_BUF_ACL_RX_COUNT 0
+#endif /* CONFIG_BT_CONN && CONFIG_BT_HCI_HOST */
+
+#if defined(CONFIG_BT_BUF_ACL_RX_COUNT) && CONFIG_BT_BUF_ACL_RX_COUNT > 0
+#warning "CONFIG_BT_BUF_ACL_RX_COUNT is deprecated, see Zephyr 4.1 migration guide"
+#endif /* CONFIG_BT_BUF_ACL_RX_COUNT && CONFIG_BT_BUF_ACL_RX_COUNT > 0 */
+
+BUILD_ASSERT(BT_BUF_ACL_RX_COUNT <= BT_BUF_ACL_RX_COUNT_MAX,
+	     "Maximum number of ACL RX buffer is 65535, reduce CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA");
+
 /** Data size needed for HCI ACL, HCI ISO or Event RX buffers */
 #define BT_BUF_RX_SIZE (MAX(MAX(BT_BUF_ACL_RX_SIZE, BT_BUF_EVT_RX_SIZE), \
 			    BT_BUF_ISO_RX_SIZE))
 
 /** Buffer count needed for HCI ACL, HCI ISO or Event RX buffers */
 #define BT_BUF_RX_COUNT (MAX(MAX(CONFIG_BT_BUF_EVT_RX_COUNT, \
-				 CONFIG_BT_BUF_ACL_RX_COUNT), \
+				 BT_BUF_ACL_RX_COUNT), \
 			     BT_BUF_ISO_RX_COUNT))
 
 /** Data size needed for HCI Command buffers. */

samples/bluetooth/mesh/boards/bbc_microbit.conf

@@ -13,7 +13,7 @@ CONFIG_BT_PERIPHERAL=n
 CONFIG_BT_EXT_ADV=n
 CONFIG_BT_RX_STACK_SIZE=1100
 CONFIG_BT_BUF_EVT_RX_COUNT=3
-CONFIG_BT_BUF_ACL_RX_COUNT=3
+CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA=1
 CONFIG_BT_BUF_EVT_DISCARDABLE_COUNT=3
 
 CONFIG_BT_CTLR_ADV_EXT=n

samples/bluetooth/peripheral_hr/prj_minimal.conf

@@ -101,7 +101,6 @@ CONFIG_BT_CTLR_PHY_2M=n
 # Reduce Bluetooth buffers
 CONFIG_BT_BUF_EVT_DISCARDABLE_COUNT=1
 CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE=45
-CONFIG_BT_BUF_ACL_RX_COUNT=2
 CONFIG_BT_BUF_EVT_RX_COUNT=2
 
 CONFIG_BT_CONN_TX_MAX=2

subsys/bluetooth/common/Kconfig

@@ -92,12 +92,21 @@ config BT_BUF_ACL_RX_SIZE
 	  An L2CAP SDU is also referred to as an L2CAP Credit-based frame or
 	  K-frame.
 
+config BT_BUF_ACL_RX_COUNT_EXTRA
+	int "Number of extra incoming ACL data buffers"
+	default 0
+	range 0 65535
+	help
+	  Number of incoming extra ACL data buffers sent from the Controller to
+	  the Host.
+
+	  By default, the number of incoming ACL data buffers is equal to
+	  CONFIG_BT_MAX_CONN + 1.
+
 config BT_BUF_ACL_RX_COUNT
-	int "Number of incoming ACL data buffers"
-	default NET_BUF_RX_COUNT if NET_L2_BT
-	default 3 if BT_RECV_BLOCKING
-	default 6
-	range 1 64
+	int "[DEPRECATED] Number of incoming ACL data buffers"
+	default 0
+	range 0 256
 	help
 	  Number or incoming ACL data buffers sent from the Controller to the
 	  Host.

subsys/bluetooth/host/buf.c

@@ -36,7 +36,7 @@ NET_BUF_POOL_FIXED_DEFINE(discardable_pool, CONFIG_BT_BUF_EVT_DISCARDABLE_COUNT,
 			  sizeof(struct bt_buf_data), NULL);
 
 #if defined(CONFIG_BT_HCI_ACL_FLOW_CONTROL)
-NET_BUF_POOL_DEFINE(acl_in_pool, CONFIG_BT_BUF_ACL_RX_COUNT,
+NET_BUF_POOL_DEFINE(acl_in_pool, BT_BUF_ACL_RX_COUNT,
 		    BT_BUF_ACL_SIZE(CONFIG_BT_BUF_ACL_RX_SIZE),
 		    sizeof(struct acl_data), bt_hci_host_num_completed_packets);
 

subsys/bluetooth/host/hci_core.c

@@ -1922,7 +1922,7 @@ static int set_flow_control(void)
 	hbs = net_buf_add(buf, sizeof(*hbs));
 	(void)memset(hbs, 0, sizeof(*hbs));
 	hbs->acl_mtu = sys_cpu_to_le16(CONFIG_BT_BUF_ACL_RX_SIZE);
-	hbs->acl_pkts = sys_cpu_to_le16(CONFIG_BT_BUF_ACL_RX_COUNT);
+	hbs->acl_pkts = sys_cpu_to_le16(BT_BUF_ACL_RX_COUNT);
 
 	err = bt_hci_cmd_send_sync(BT_HCI_OP_HOST_BUFFER_SIZE, buf, NULL);
 	if (err) {

subsys/bluetooth/host/l2cap.c

@@ -39,7 +39,7 @@ LOG_MODULE_REGISTER(bt_l2cap, CONFIG_BT_L2CAP_LOG_LEVEL);
 #define L2CAP_LE_MIN_MTU		23
 #define L2CAP_ECRED_MIN_MTU		64
 
-#define L2CAP_LE_MAX_CREDITS		(CONFIG_BT_BUF_ACL_RX_COUNT - 1)
+#define L2CAP_LE_MAX_CREDITS		(BT_BUF_ACL_RX_COUNT - 1)
 
 #define L2CAP_LE_CID_DYN_START	0x0040
 #define L2CAP_LE_CID_DYN_END	0x007f

subsys/bluetooth/host/rfcomm.c

@@ -37,7 +37,7 @@ LOG_MODULE_REGISTER(bt_rfcomm);
 #define RFCOMM_MIN_MTU		BT_RFCOMM_SIG_MIN_MTU
 #define RFCOMM_DEFAULT_MTU	127
 
-#define RFCOMM_MAX_CREDITS		(CONFIG_BT_BUF_ACL_RX_COUNT - 1)
+#define RFCOMM_MAX_CREDITS		(BT_BUF_ACL_RX_COUNT - 1)
 #define RFCOMM_CREDITS_THRESHOLD	(RFCOMM_MAX_CREDITS / 2)
 #define RFCOMM_DEFAULT_CREDIT		RFCOMM_MAX_CREDITS